Color Hardcopy Technology: Plotters and Printers Daniel Lee INTRODUCTION Raster Device: Output is an array of dots. Resolution is determined by the dot density, size of the dots, and There is such a wide range of plotters and printers accuracy of dot placement. Resolution is specified as available in taday's market that people purchasing color the number of distinguishable dots that can be placed hardcopy devices need to understand the features and along a linear measure; usually I inch. A line would be benefits that different hardcopy technologies offer. a ray of dots. Raster devices can also control the color Today. color graphics systems are more widely available of each dot. and easier to use. The increased availability of color technology is helping people obtain the benefits that Line quality in a vector device depends on the color graphics can provide. combination of - addressable and mechanical resolution. Figure 2 shows how a vector line is drawn. When a pen Color helps present complex information by adding plotter draws a line between points A and B, it is another dimension to graphics. Recent academic studies actually drawin~ to the points on a grid between A and have shown that using color graphics leads to greater B. The grid POlDts are the points that are electronically comprehension and retention of information, which in addressable by the plotter. The spacing between grid tum leads to more persuasive presentations. Color points equals the addressable resolution. A typical graphics turn data into information by showing trends, addressable resolution for pen plotters is 0.00 I inches. patterns, and inter-relationships. Using color graphics can shorten meetings, save time analyzing data, and Most vector devices have mechanical resolution equal to improve decision making. addressable resolution. If the mechanical resolution is lower than the addressable resolution, then the pen This paper reviews color plotter and printer technology. plotter can not physically move the pen to all the This information can be used within the framework addressable points (i.e. the smallest pen move mechani­ developed in "A Guide to Color Hardcopy Device cally possible would be greater than the distance to the Purchases," presented at SUGI-12. to help evaluate a nearest addressable point). Mechanical resolution is color hardcopy device. This technology review will help more difficult to control and plotters with higher users understand how different hardcopy devices can mechanical resolution will be more expensive. meet their needs for a color graphics solution. Two other measures of vector line quality are repeata­ bility and accuracy. Repeatability refers to a vector GROWTH IN THE COLOR HARDCOPY MARKET device's ability to move a pen to a pre-determined point. Poor repeatability is noticeable in circles that do The wide variety of hardcopy devices available is due to not close. and connecting lines that do not meet. the rapid growth of color graphics applications. The Accuracy refers to how exactly a vector device can growth in the color hardcopy market can be linked to position one endpoint with respect to another point. greater use of color monitors, more powerful computer Accuracy is specified as the maximum distance between systems at lower prices, and greater software support for the desired endpoint and the actual endpoint drawn. color devices. An end-user survey by CAP Internation­ Poor accuracy is noticeable when parallel lines do not al showed a significant increase in the use of graphics between 1986 and 1988. CAP International's survey also appear parallel (exact spacing between two lines). showed that the leading technologies in end-users' Resolution in a raster device depends on the density~ future purchasing plans are pen plotters, laser printers, accuracy. and size of the dots placed. Line quality is ink jet printers, and electrostatic plotters. influenced by the angle or shape of the line. Horizontal Manufacturers have responded to this growth by and vertical lines appear smooth. However. angled lines producing more sophistocated color hardcopy devices at will have jagged edges due to the dot placement needed lower prices. More intelligence is being built into to form the line. Manufacturers improve line smooth­ hardcopy devices to reduce processing burdens on ness by increasing the dot density (dots/inch) or by software. There are more color printers that use plain increasing the accuracy of dot placement. A dot can paper, with higher resolutions. The availability of color actually be placed on top of the intersection of two dots copiers has also made it easier to reproduce color using a technique known as anti-aliasing. Covering that intersection results in a smoother line. Both alternatives hardcopy. of increasing dot density and placement accuracy result in higher hardware costs. and longer times to process an COLOR HARDCOPY TECHNOLOGY image. Color hardcopy technology can be categorized into Vector color hardcopy devices produce superior line impact and non-impact devices. Impact devices are graphics such as charts and graphs, but their color dot-matrix printers and pen plotters. Non-impact capabilities are limited to the colors of the pens. Raster devices are ink jet printers, thermal transfer printers, devices produce complex images and shapes better due electrostatic plotters, and electrophotographic/laser to their ability to control individual dot placement. printers. Dot matrix printers and pen plotters are in Since raster devices can also control the color of wide-spread use, and currently dominate the market for individual dots, they have color capabilities, such as hardcopy devices. However, non-impact devices will shading, which are not possible in a vector device. have the ~reatest growth over the next 5-10 years due to advances m technology. All raster color hardcopy devices use a subtractive color system to produce output. Printed colors are created by Another way to categorize color hardcopy devices is by colorants that absorb certain colored light, and transmit vector vs raster technology. Vector or raster technology the remaining light. The subtractive color system is refers to how an image is drawn on the media/paper. based on the primary colors cyan, magenta, yellow, Figure I shows the difference between lines drawn on (CMY) which absorb their complementary colors red, vector devices and raster devices. Pen plotters are blue, and green (RGB). When a surface is coated with a vector devices and most printers are raster devices. cyan colorant, the colorant absorbs all the red light and Simple definitions of the two techniques are: the remaining light is reflected from the surface. Using a system of three primary colors (CMY), a total Vector Device: Creates lines by drawing between two of 7 colors can be produced when ink dots are end points. Resolution is determined by how closely the superimposed on each other. The cyan, magenta, and device can hit the two end points. Resolution is defined yellow dots can be superimposed to create red, blue, as addressable and mechanical resolution. Addressable green, and black. Each colored dpt represent~ a picture resolution defines how small of a move is electronically element (pixel) in the hardcopy Image. A WIder range recognized. Mechanical resolution defines how small of of color can be created by placing dots next to each a move can be mechanically or physically made. other. The colored dots are -so small that the individual 411 elements cannot be resolved. Light reflected from the Dot matrix printers are used when people want fast a?jacent colors is mixed in the observer's eye to create a color hardcopy and they do not care about the resolution smgle color. or quality of the output. Color dot matrix output is not widely used for presentations. Dot matrix printers are yigure 3 shows how dots can be placed in a matrix to primarily being used with spreadsheet applications. The !ncrease the numb~r of c~lor combinations. Placing dots advantages o.f. dot matrix printers are their very low C?st, and ablhty to work yvlth plain paper. The main lfl a. 2xf superplXel Will create 330 possible color combmatIons. However, the 2x2 superpixel has in­ dIsadvantages of dot matrIX printers are their limited creased the effective dot size from I dot to 2 dots and color capabilities, and noisy operation. the effective resolution of the hardcopy will drop by the sam.e fac.tor. Usi~g a 2x2 superpixel on a 400 dpi deVice wIll effectIvely lower the resolution to 200 dpi Ink Jet Printers Larger superpixels increase the number of colors that can be produced. but the tradeoff is lower resolution. Ink jet printers produce color hardcopy by spraying a stream of ink droplets from a multi-nozzle head onto The accuracy of color reproduction is measured by color' the media. Th.e ink jets are moved relative to the paper hue, saturahon, and brightness. Color hue refers to the to create multi-color images and characters in a single wavelength in the light spectrum at which a particular pass. A continuum of color is achieved by spraying c.olor absorbs light. Saturation refers to the amount of color dots so small that the individual elements cannot Itg!'t that a color reflects (soft vs intense colors). be resolved. Light reflected from the adjacent colors is Bnghtness refers to the total amount of light reflected. mixed in the observer's eye to create a single color. A The ultimate goal of color reproduction is to create as range of color is achieved by varying the pattern and realistic an image as possible. Manufacturers of color amount of each color. hardcopy devices f ccus on resolution, range of color and accuracy of color. • There are two general systems for generating ink droplets; continuous stream, and drop-on-demand systems.